The pharmacokinetics of morphine in pediatric cancer patients receiving continuous, long-term intravenous or subcutaneous infusions of morphine has been studied. Continuous morphine infusions have provided effective pain control which was not achievable with regularly scheduled bolus administration. Analysis of the pharmacokinetic data has shown a linear relationship between infusion rate and plasma concentration over a wide dosage range and that subcutaneous administration yields similar plasma levels to intravenous administration. Compartmental modeling of morphine infusion data using pharmacokinetic data parameters from bolus injections was also found to be possible. Finally, CSF levels were found to be roughly comparable to plasma levels for the limited number of samples obtained.